The background of the invention will be set forth in two parts.
1. Field of the Invention
This invention relates to dimensionally stable support structures and more particularly to such structures for support of optical sensors, large antennas, and the like.
2. Description of the Prior Art
Advanced satellite missions and also ground-based applications require extremely precise and dimensionally stable structures for support of optical sensors or antennas, for example. In the past, various techniques have been developed in efforts to overcome the problem which generally stems from temperature gradient effects in materials, causing non uniform expansion or contraction.
One such technique is designed to compensate for temperature gradient effects across the cross sectional dimension of hollow tubular members. Here, holes are drilled or otherwise provided along the surface of a side of the structure which generally faces a heat source, such as the sun. The purpose of this is so that the sun's energy that passes through the holes heats up the opposite side of the tubular member and lessens the temperature gradient across the member. This, of course, helps to lessen the rate of dimensional change in the areas of the holes. However, in all areas of the structure not immediately adjacent to the holes, there is no compensation. The average temperature of such a member is not reduced by this scheme and therefore distortions are still high. In addition, such a scheme makes it very difficult to even predict what the overall dimensional distortions will be, not to mention the weakening of the structure by the holes.
Another technique is to try to provide longitudinal stability in support structures by using materials, such as Invar which exhibit relatively low coefficients of thermal expansion. However, where the support member has any significant longitudinal dimension, the temperature gradient along the length of the member will indeed be significant and consequently detrimental to dimensional stability.
Unlike the prior art, the present invention utilizes a novel technique for providing temperature insensitivity to support structures by combining the use of a material such as a graphite composite, for example, with an integral heat pipe as a thermal control device which ensures negligible temperature gradients.